September 13, 2006
02:00 PM (EDT)

News Release Number: STScI-2006-44

Tracing the Evolution of the First Galaxies in the Universe

September 13, 2006: A systematic search for the first bright galaxies to form in the
early universe has revealed a dramatic jump in the number of such
galaxies around 13 billion years ago. These observations of the
earliest stages in the evolution of galaxies provide new evidence
for the hierarchical theory of galaxy formation -- the idea that large
galaxies built up over time as smaller galaxies collided and merged.
Astronomers at the University of California, Santa Cruz, used NASA's
Hubble Space Telescope to explore the formation of galaxies during the
first 900 million years after the Big Bang. They reported their latest
findings in the September 14 issue of the journal Nature.
Deep observations in three dark patches of sky -- the Hubble Ultra Deep
Field and the Great Observatories Origins Deep Survey fields -- gathered
the faint light emitted 13 billion years ago by stars in primeval galaxies.
Only the brightest galaxies could be detected at such great distances.
The researchers observed hundreds of bright galaxies at around 900
million years after the Big Bang. But when they looked deeper, about
200 million years earlier in time, they only found one. Relaxing their
search criteria a bit turned up a few more candidates, so there must have
been a lot of merging of smaller galaxies during those 200 million years.

This panel shows four candidate galaxies that are likely to have
redshifts of 7 and thus have emitted their light when the universe
was just 750 million years old. Astronomers can determine when light
was emitted from a distant source by its redshift, a measure of how
the expansion of the universe stretched the wavelengths of the light
as it traveled through space across vast distances.